Frequency mixing passive transponder

1. A transponder device, receiving a plurality of waves having differing frequencies, and producing a modified wave therefrom, having a frequency differing from each of the plurality of received waves, and having characteristic distinguishing modifications, said device comprising: a mixer, receiving a plurality of waves and producing therefrom a mixed wave having a frequency differing from the plurality of waves; a wave modifying device, operating to characteristically modify a wave by one or more methods selected from the group consisting of sequentially modulating the wave with a plurality of modulation states and modulating the wave according to a transfer function having a plurality of distinct parameters; said wave modifying device and said mixer in combination forming a network for producing a wave derived from the received plurality of waves, which is both characteristically modified by said wave modifying device and having a frequency of the mixed wave, said network being arranged with either said characteristically modified wave being one or more of the plurality of waves received by said mixer, or the characteristically modified wave being received derived from the mixed wave from said mixer, or both; and an output, for emitting the characteristically modified wave externally from said transponder device.

2. The transponder device according to claim 1, wherein said network is arranged such that said wave modifying device receives the mixed wave from said mixer.

3. The transponder device according to claim 1, wherein said network is arranged such that said wave modifying device receives one or more of the plurality of received waves, said mixer receiving the characteristically modified wave from said wave modifying device.

4. The transponder device according to claim 1, further comprising an antenna system, receiving the plurality of waves as electromagnetic waves in space.

5. The transponder device according to claim 4, wherein said antenna system comprises an antenna element adapted to receive at least two of the plurality of waves.

6. The transponder device according to claim 4, wherein said antenna system comprises at least two antenna elements, each being adapted to receive a different frequency component of the plurality of waves.

7. The transponder device according to claim 1, wherein said mixer comprises a semiconductor.

8. The transponder device according to claim 7, wherein said semiconductor device comprises a two terminal device.

9. The transponder device according to claim 7, wherein said semiconductor device comprises a device having at least three terminals.

10. The transponder device according to claim 1, wherein said wave modifying device comprises an electroacoustic transducer.

11. The transducer device according to claim 1, wherein said wave modifying device comprises a semiconductor modulator.

12. The transducer device according to claim 1, wherein said wave modifying device comprises a control input, controlling a transimpedance of a semiconductor modulator and said mixer comprises a conduction channel of said semiconductor modulator.

13. The transducer device according to claim 1, wherein the wave which is both characteristically modified and at a frequency of the mixed wave is emitted through a common antenna element which also receives at least one of the plurality of received waves.

14. The transponder device according to claim 1, wherein said transponder device is adapted to receive and modify the plurality of waves and wherein at least one of the plurality of received waves has a frequency which varies over time.

15. A communication method, comprising the steps of: providing a transponder device, for receiving a plurality of waves having differing frequencies, and producing a wave derived therefrom, having a frequency differing from each of the plurality of received waves and having characteristic modifications, the transponder device having an antenna system for receiving the plurality of waves having differing frequencies and emitting the wave, having a frequency differing from the plurality of received waves and having characteristic modifications: exciting the transponder device with a plurality of waves having differing frequencies; producing a wave in the transponder device having characteristic modifications and a frequency differing from each of the plurality of received waves by one or more methods selected from the group consisting of sequentially modulating the wave with a plurality of modulation states and modulating the wave according to a transfer function having a plurality of distinct parameters; and detecting the wave, having a frequency differing from the plurality of received waves, and having characteristic modifications.

16. The method according to claim 15, wherein the transponder device comprises a mixer and a wave modifying device.

17. The method according to claim 16, further comprising the steps of mixing the plurality of waves received by the antenna system in a mixer and modifying the mixed plurality of received waves in a wave modifying device.

18. The method according to claim 16, further comprising the steps of characteristically modifying at least one of the plurality of received waves with a wave modifying device and mixing the characteristically modified wave with at least one of the plurality of received waves in a mixer.

19. The method according to claim 15, further comprising the step of receiving at least two of the plurality of waves with a single antenna element.

20. The method according to claim 15, further comprising the step of receiving at least one of the plurality of waves with each of at least two different antenna elements, each respective antenna element being adapted to receive at least one different frequency wave.

21. The method according to claim 16, wherein the frequency differing from each of the plurality of received waves is produced by a semiconductor mixer.

22. The method according to claim 15, further comprising the step of producing a wave, having a frequency differing from the plurality of received waves, by passing at least two of the plurality of received waves through a nonlinear conductance device.

23. The method according to claim 15, further comprising the step of producing a wave, having a frequency differing from the plurality of received waves, by modulating a transconductance of a semiconductor device conducting a wave having a first frequency with a wave having a second frequency.

24. The method according to claim 16, further comprising the step of acoustically transducing at least one wave for characteristic modification thereof.

25. The method according to claim 15, further comprising the step of characteristically modifying a wave with a semiconductor modulator.

26. The method according to claim 15, wherein the step of producing a wave in the transponder device having characteristic modifications, comprises passing a plurality of waves through a semiconductor device having a control input, a transimpedance of a conduction channel being controlled to provide characteristic modifications thereof and the differing frequency wave being generated by a nonlinear conduction characteristic of the conduction channel of the semiconductor device conducting waves having at least two different frequencies.

27. The method according to claim 15, further comprising the step of emitting the characteristically modified wave having a frequency differing from the plurality of received waves through a common antenna element which also receives at least one of the plurality of received waves.

28. The method according to claim 15, wherein said transponder device is adapted to receive a plurality of waves, at least one of which varies in frequency over time and to produce a wave which is characteristically modified, further comprising the step of varying a frequency of at least one of the received waves over time.

29. The method according to claim 15, further comprising the steps of: emitting the plurality of waves having differing frequencies with an interrogator system into an interrogation region, said detecting step comprising: receiving the wave having a frequency differing from the plurality of received waves, and having characteristic modifications from the interrogation region; and analyzing the received wave to extract characteristic information identifying the respective transponder.

30. The method according to claim 29, wherein the wave having a frequency differing from the plurality of received waves is within the 900 MHz 1SM band.

31. The method according to claim 29, wherein at least one of the plurality of waves has a non-stationary frequency, and wherein the plurality of waves, when mixed together, produce a significant signal component in the 900 MHz frequency band having a non-stationary frequency.

32. The method according to claim 29, wherein the wave having a frequency differing from the plurality of received waves is a 900 MHz band signal component having a non-stationary frequency.

33. The method according to claim 29, wherein said analyzing step analyzes wave having a frequency differing from the plurality of received waves for characteristic delay encoding patterns.

34. A transponder device, receiving a plurality of radio frequency waves having differing frequencies, and producing a modified wave derived therefrom, having a frequency differing from each of the plurality of received waves, and having characteristic modifications capable of being distinguished from waves of the same frequency having differing characteristic modifications, said device comprising: an antenna system for receiving the plurality of radio frequency waves and transmitting the modified wave; a mixer, receiving a plurality of waves from said antenna system and producing a mixed wave having a frequency differing from the received plurality of waves; a wave modifying device, receiving the mixed wave from said mixer and producing the modified wave derived therefrom, having a transfer function selected from one or more of the group consisting of a characteristic set of identifying transfer function coefficients and a characteristic time sequence of identifying symbols, the modified wave being returned to said antenna system for transmission.

35. The transponder device according to claim 34, wherein said wave modifying device returns the modified wave to said antenna system through said mixer.

36. The transponder device according to claim 34, wherein said transfer function is a characteristic set of identifying delay coefficients.

37. The transponder device according to claim 34, wherein said transfer function is a characteristic time sequence of identifying symbols.